Heating unit for mechanical refrigerators and the like



R U R Q 11 R E m. S m 0 N f! I I l l l I l l l \!.r\l w m G r WHM W III I W W b\ N I 1\ m N R r l ||4 I .M m l l I I I I I! 1 T Ill L R W N m 0 w i a m N N I & om V k 67 Sept. 22, 1959 v. K. WAGNER, JR

HEATING UNIT FOR MECHANICAL REFRIGERATORS AND THE LIKE Filed Feb. 21, 1957 United States Patent HEATING UNIT FOR MECHANICAL REFRIGERA- TORS AND THE LIKE Victor K. Wagner, Jr., Suflield, Conm, assignor to Springfield Wire d: Tinsel Company, Springfield, Mass, a corporation of Massachusetts Application February 21, 1957, Serial No. 641,521 1 Claim. (Cl. 338210) This invention relates to electrical resistance heaters and more particularly to such heaters which are positioned at critical positions in the interior of mechanical refrigerators to prevent the formation of ice, to effect evaporation of moisture resulting from the defrosting of such refrigerators, and in relation to the operating parts or controls, such as the capillary tube of the control mechanism which governs the box temperature.

The heat supplied by these heaters prevents condensed moisture from freezing, and a part of such moisture remains in contact with the heater in liquid form. For this reason it is necessary for the heater to be completely water-tight since leakage into the electrical Wiring could result in an electrical shock being experienced by the user of the appliance. Previous heaters used for this purpose suffered from this drawback, which is overcome in the present invention. For that reason the presently available heating units have proved unreliable and costly.

It is the principal object of the present inventipn to provide a construction for such heater units which will remain moisture-tight under all working conditions for substantially the life of the refrigerator and which is simple and economical to manufacture and install.

It is a further object to provide a heater construction having the above advantages which is applicable to the various forms of heaters needed for mechanical refrigerator purposes and capable of such dimensional variations as various refrigerator manufacturers may desire.

A. further object of the invention is to provide a con struction which can be economically manufactured to meet such varied dimensional specifications using conventional molding techniques.

Other and further objects and advantages will be made apparent in the disclosures of the accompanying drawing and in the following specification and claims.

In the accompanying drawing,

Fig. 1 is a plan view, parts being broken away, of one form of heater embodying the invention;

Fig. 2 is an end elevational view of the structure of Fig. 1, looking from the right of Fig. 1;

Fig. 3 is a fragmentary View similar to Fig. 1 but illustrating a modified procedure for providing the structure of Fig. 1;

Fig. 4 is a view similar to Fig. 1 but showing a structure modified as to dimensional arrangement and illustrating the structural flexibility of the invention in meeting the specifications of refrigerator manufacturers;

Fig. 5 is a front elevational view of the structure of Fig. 4;

Fig. 6 is an end elevational right of Fig. 5;

Fig. 7 is a diagrammatic plan View on a reduced scale of a further modified form of heater, employing a plurality of loops; and

Fig. 8 is a detail view on a greatly enlarged scale of a fragmentary length of the resistance strand unit.

each instance the heater comprises a resistance heating unit generally indicated at 1, lead wires generally view looking from the indicated at 2 for supplying electrical current to the heating unit, means generally indicated at 3 for connecting the ends of the lead wires 2 to the ends of the heating unit 1 and a unitary casing generally indicated at 4 which encloses the elements 1, 2 and 3.

The casing 4 is formed of a material which provides both electrical insulation for the surrent carrying elements and protection against the entrance of moisture as as well as resistance to deterioration from the high temperatures generated in the heating unit. For the purposes of the invention I have found silicone rubber to be the preferred material. Silicone rubber is produced by compounding elastorneric silicones with vulcanizing agents and fillers. Silicone is a generic term embracing as a class all organopolysiloxanes, the latter being made up of a molecular skelton of silicon-oxygen linkages with organic groups completing the molecule. Depending on its structure and composition a silicone may be fluid, resinous of elastromeric and the elastomerics are compounded with vulcanizing agents and fillers to produce a variety of silicone rubbers. A silicone rubber is therefore defined as a vulcanizable elastomeric organopolysiloxane compound. Various grades of silicone rubber are available from General Electric Company, Dow Corning Corporation and others. General Electric silicone rubber 740 and Dow Corning DC. 50 are examples of silicone rubbers satisfactory for material forming the casing.

The heating unit 1 comprises a length of a flexible strand of resistance material comprising a core 5 formed of a multiplicity of twisted or braided fine glass fibers about which is spirally Wound a fine resistance Wire 6 of any suitable metal or metal alloy, as indicated at 6. Nickel-chromium-iron alloy is a preferred material for the coil 6. Before the resistance wire 6 is wound on the core 5' the latter is impregnated with a silicone resin such as Dow Corning 40C. The silicone resin provides a flexible matrix for the glass filaments and prevents undesirable slipping of the windings on the surface of the core and a stranded resistance coil is thus provided which has the strength, physical characteristics, and flexibility which in combination with the physical characteristics of the silicone rubber casing provides a heating unit which, as later pointed out, ideally meets the requirements of refrigerator manufacturers.

Referring more particularly to Figs. 1, 2 and 3 the lead wires 2 are insulated as at 8 with silicone rubber of the type, such as Dow Corning DC. 50 used for the casing 4. The heating element 1 is shown formed into an elongated loop 9 and the ends of the lead wires 2 are electrically connected to the ends of the looped resistance element 1 as by conventional small metal clamps indicated at 3. The loop 9, connections 3 and the adjacent insulted end portions of the lead wires are covered with silicone rubber and the covering molded by heat and pressure to enclose the resistance element 1, connections 3 and the lead wires 2 in a completely unit-ary homogeneous casing 4 of silicone rubber. While for purposes of illustration the insulation 8 of the lead wires 2 and the body portion of the casing enclosing the loop 9, connections 3 and covering the adjacent end portions of the lead wires are distinguished by the cross hatching, it will be understood that following the molding operation the silicone rubber of the body portion and the portion of the insulation 8 covered thereby coalesce into a single body so that the insulation of the lead wires becomes an integral part of the casing. In the form of Figs. 1 and 2 the casing may be considered as of minimum thickness, that is the amount of silicone rubber covering and separating the current carrying elements and providing insulation for the lead wires is only sufficient to meet the safety standards set up by authoritative codes such as those of Underwriters Laboratories, Inc. and allow for manufacturing tolerances needed to assure that such standards are met. The heater of Figs. 1 and 2, may have any desired length and, as shown in Fig. 2, the main portion of the heater is in the form of a fiat relatively narrow flexible portion 10.

As illustrated in Fig. 3 a heater substantially identical with that of Figs. 12 may be formed by insulating the stranded resistance unit 1 with silicon rubber, as indicated at 11, in the same manner as the lead wires are insulated at 8. The desired length is then cut from the so insulated resistance strand, the length bent or folded to form a loop the ends of the lead wires connected to the ends of the resistance strand by clamp 3, the connected and adjacent portions of the lead wires and strand covered with a quantity of silicone rubber as at 12 and the insulation of the strand, covering 12 and the adjacent insulation 8 integrated by molding as previously described.

As above mentioned the actual shape of the heater will be made to conform to the specifications of the refrigerator manufacturers and will depend on the design of the members of the refrigerating system, their dimensions, the space made available for the heater, the specific function it is to perform and the nature of the clips or other means which are used to secure it in place. These manufacturers requirements are met by suitable shaping of the mold cavity in which the material of the casing is integrated into unitary form.

By way of example a relatively short thick, less flexible heater is shown in Figs. 4, 5 and 6 which follows the general procedure of Fig. 1 in its assembly. As there shown the main body portion 15 of the casing 4, as Well as the portion 16 which encloses the connections, are shown as generally rectangular in cross section, and a band of fabric or plastic tape 17, or other abrasive protection is applied to the casing rearwardly of the resistance element to prevent abrasion of the casing where the leads extend through a wall opening or are engaged by a clamp.

In some cases the resistance strand may be bent into a multiloop form in a common plane as indicated at 20 in Fig. 7, where the body of the casing is shown in the form of a sheet 21 in which the loops are embedded, the

connections 3 and the adjacent end portions of the lead wire insulation 8 being covered by a portion 22, insulation 8, and portions 22 and 21 being integrated into a unit by molding as previously described.

in any case a completely integral casing is formed which completely encloses the heating element, its connections to the lead wires and the lead wires, the easing in effect extending to the free ends of the lead wires, where the insulation may be stripped back in the usual manner, as indicated at 18, and tinned if desired to provide for their connection to the main power line of the refrigerator. The outer shape of the body of the heater will be determined by the shape of the mold cavity which will be determined by and conform to the particular refrigerator service for which the heater is required and the thickness and form of the body portion of the casing is not, of course, limited to minimal insulation require ments but will be shaped and dimensioned to perform the structural functions above mentioned.

What is claimed is:

An electrical resistance-heating unit for use in the interior of mechanical refrigerators and the like which comprises a flexible continuous resistance strand having a glass fibre core impregnated with a silicone resin about which is wound a spiral coil of resistance wire, said strand being arranged in a parallel arm loop formation, means connecting the ends of the loop to respective lead wires for supplying current to the loop, said lead wires, connecting means and loop being encased in silicone rubber molded to form an integral moisture-proof insulating casing for said lead wires, connecting means and loop, the portion of the molded casing containing the loop being flexible and spatulate in shape.

References Cited in the file of this patent UNITED STATES PATENTS 2,251,697 Van Daarn et al. Aug. 5, 1941 2,387,829 Bnrnham et al Oct. 30, 1945 2,585,443 Cox Feb. 12, 1952 2,610,286 Cox Sept. 9, 1952 2,628,300 Berkelhamer Feb. 10, 1953 2,659,795 Boggs Nov. 17, 1953 

